In recent years, there has been an increase in research and development about a radio communication system, hereinafter referred to as “Sensor Net”, in which a terminal having a sensor and radio or wireless communication function, hereinafter referred to as “sensor node”, is used to capture various information pieces of the real world into an information processing device in real time. Sensor nodes are placed everywhere and set on everything, and information pieces gathered by the sensors are sent to a network. The data so gathered are processed into various forms, and fed back to the real world. Such Sensor Net has been under consideration about applications to various fields such as logistics, healthcare, and quality control.
To set a sensor node without the need for selecting where to put it, the network connection through a wireless communication and the downsizing thereof are de rigueur. However, a compact-size sensor node is restricted in the capacity of its battery. Hence, taking into account the operational cost including the replacement of a battery, to reduce its power becomes a challenge. For example, Non-patent Document presented by Yamashita, S. et al., “A 15×15 mm, 1 μA, reliable sensor-net module: enabling application-specific nodes,” Information Processing in Sensor Networks, 2006. vol., no., pp. 383-390, 19-21 Apr. 2006, discloses a technique for performing the power reduction by bringing a micro controller unit, hereinafter referred to as “MCU”, to its standby state, and using a timer placed outside MCU to restore it.
In addition, lots of researches on the reduction in power consumption of electronic devices have been made. For instance, Japanese Unexamined Patent Application Publication No. JP-A-9-128106 discloses a central processing unit (CPU) having three operation modes, i.e. a normal mode, a power-saving mode lower in power consumption in comparison to the normal mode, and a stop mode in which an action is stopped completely.